An office chair is a well-known piece of furniture that allows a user to comfortably sit in the chair while performing various work tasks. Manufacturers of office chairs have always faced a difficult task when trying to produce an office chair that will be suitable for a broad variety of different people. One reason for this difficulty is that users of chairs vary greatly in their relative size and proportions. The heights of users, for example, can vary significantly, with some users being taller while others are shorter, and some users having longer trunk proportions while others have longer leg sections. In addition, the size of users varies, with some being larger while others are smaller. Another difficulty that manufacturers must consider is the wide variety of tasks that different users perform in their office chairs. Although many users perform similar tasks in their chair like working on a computer, writing at a desk, or reading documents, the work environment and the type of individual user can vary greatly. For example, the tasks performed while sitting in a chair can differ considerably between workers in a factory, a home-office, or at an administration center. Different types of users, like executive workers and staff workers, also have different requirements for their chair.
Notwithstanding these difficulties, the most difficult issue that manufacturers must confront is the various preferences of individual users. Seldom do the individual preferences of different users coincide exactly. Often a user will generate strong personal opinions about an office chair as a result of the long periods of time in which the user sits in the chair and the direct intimate contact that the user has with the chair. To a large extent, manufacturers have been forced to address this wide range of personal preference by providing many different chair designs so that different users can choose a chair that satisfies their particular preferences. At the same time, manufacturers strive for designs which are cost effective to produce and which will satisfy as many users as possible.
One preference that all users share is a desire for an office chair that is comfortable. One feature that chair manufacturers often include to make a chair more comfortable is a tilt mechanism. This mechanism allows the back of the chair to recline rearward when the user applies pressure with his upper body to the back of the chair. This allows the user to relax in a more laid back, fully supported position. Typically, a range of about 20° of rearward travel is commonly provided, with a constant amount of pressure required to recline the back throughout the travel range.
One reclining system that is commonly used for office chairs involves a single pivot between the stem of the chair and the seat and back assembly. Typically, the pivot is located beneath the seat and behind the front edge of the seat. In this system, the seat and the back are rigidly attached to each other so that the back is oriented approximately 90° in a vertical direction from the seat. A spring is then provided to bias the seat and back assembly forward into an unreclined position in which the seat is approximately horizontal to the floor and the back is approximately vertical. When the user applies pressure to the back of the chair, the pivot and spring allow the seat and the back to rotate rearwardly together around the pivot. Some users find this reclining system undesirable, however, because of the rigid attachment of the seat and the back. One especially undesirable result of this reclining system is that the front edge of the seat moves upward as the back is reclined. Because the seat and the back are rigidly attached to each other, the rotating movement of the seat and back assembly around the pivot causes the front edge of the seat to move upwards from its unreclined position. This upward movement places pressure on the underside of the user's legs and can lift the user's legs slightly off the floor.
To resolve this problem of seat movement during reclining, other chairs provide a fixed placement of the seat. The back is then reclined rearward independently of the seat. These systems, however, produce friction and pulling between the back of the chair and the user's upper body because the back generally travels along a different angular rotation than the user's upper body. As a result, the user usually feels an upward pulling on his clothes as he reclines.
A more desirable reclining system allows the seat to move during reclining, but at a different rate of travel than the back. One challenge in designing these types of reclining systems is achieving an optimal balance between the seat movement and back travel during reclining. The system must also be cost effective and simple to manufacture. One desirable way to reduce the cost of a reclining system is to minimize the number of parts that are required in the assembly. In addition, another way to reduce costs is to design the reclining system so that it is easy to assemble. This ease of assembly has become increasingly important recently as chair manufacturers have begun to ship chairs unassembled directly to end users. Thus, the reclining system should be capable of being assembled without needing numerous special tools. Finally, the reclining system must be durable so that it can survive over a long lifetime without failure in a variety of work environments.
One problem with some reclining systems is that the leverage applied to the main spring changes as the back is reclined rearward. For example, in some systems a greater amount of leverage is applied when the back is reclined rearward than when the back is upright. This results in the user feeling less support from the back the further the user reclines rearward. To compensate for this characteristic, some chairs have provided assist springs to supplement the reclining pressure provided by the main spring. The assist springs, however, must be cost effective and simple to install. Desirably, the assist springs can be integrated into the reclining system without a significant number of special features required to add the assist springs.
Another feature that manufacturers commonly provide on office chairs to improve comfort is a height adjustment system for the seat and the back. This feature is especially important because the length of different users' legs varies greatly. Generally, users prefer to adjust the height of their chair so that their feet rest flat on the floor and their upper legs are parallel to the seat. Often, however, a chair is used by a variety of different people, who each have their own preferred height for the seat. This is especially true of chairs that are shared by many people, such as conference room chairs. Because the height of these chairs must be changed frequently by many different people, the adjustment system should be capable of being changed quickly without requiring time consuming adjustments. The height adjustment system should also be simple to operate so that temporary users will be able to quickly learn how to change the height of the seat without becoming confused.
Commonly, office chairs have included adjustable cylinders in the stem of the chair to provide the desired height adjustment. These cylinders generally employ a valve stem that is oriented horizontally, or parallel, to the floor. Thus, in order to release the cylinder to allow the height of the chair to be adjusted, an actuating system is provided that actuates the horizontal valve stem upward and downward. However, in these systems the vertical positioning of the actuating system in relation to the horizontal valve stem is usually quite critical. This typically makes the manufacturing and assembly of the height adjustment system more expensive and complicated. The manner of using these systems can also become complicated, thus confusing the user as he attempts to adjust the height of the chair.
Generally, reclining systems provide the desired reclining pressure to the back with a spring that is increasingly stressed as the back is reclined rearward. Because individual users commonly prefer different amounts of reclining pressure, manufacturers typically provide a spring adjustment system that can be used by the user to increase or decrease the amount of reclining pressure. The spring adjustment system usually includes a screw that can be turned by the user, thereby moving a spring guide that increases or decreases stress in the spring. Generally, manufacturers install the spring into the reclining system with a small amount of initial stress introduced into the spring when the adjusting screw is turned to the lowest pressure setting. Therefore, the user is prevented from relieving the entire stress in the spring when the adjusting screw is turned. This preload stress is desirable because an unstressed spring will tend to rattle in the reclining system when the chair is moved about. The back of the chair will also be loose and will flop in the upright position between the forward stop and the spring. In addition to these problems, some spring adjustment systems require a minimum amount of spring pressure at all times in order to function properly.
Typically, manufacturers introduce the preload stress into the spring either manually or with special tools while the spring is being installed into the reclining system. Thus, in the case of some spring assemblies, a force as high as 100 lbs may need to be applied to compress the spring during installation. This combined procedure of compressing the spring while simultaneously installing the spring into the reclining system can become quite difficult and time consuming. This procedure is also undesirable for chairs that are shipped unassembled directly to end users who may not have the special tools necessary to install the spring with the necessary preload stress. Thus, a system for easily introducing an initial preload stress into the spring is desirable.
To provide further comfort for the user, manufacturers often provide arm rests on the chair so that the user can conveniently rest his forearms. Other users, however, prefer not to have arm rests on their chairs because the arm rests can obstruct the sides of the chair and can interfere with free movement into or out of the chair. Chairs without arm rests are also preferred to save costs when the chair will be used infrequently.
Thus, a modular arm rest system is desirable to allow chairs to be provided with or without arm rests. Desirably, this system would include a reclining chair and a four-legged stacker chair. A modular arm rest system such as this could increase the number of chair configurations possible and could minimize costs by using common components or components with similar functions. The arm rest system, however, must provide a rigid, secure attachment to the chair frame in order to satisfy the user's expectations of quality. In addition, the arm rest system should be simple and easy to install to allow users to install or remove the arm rests themselves. Finally, an arm rest system that allows users to reconfigure a chair later after initial assembly of the chair would be preferred.
One area of the chair that has a significant impact on a user's satisfaction with the chair is the seat. The seat is the surface upon which the user rests his buttocks, and as such, the seat directly influences the overall comfort of the chair. Generally, users prefer a seat that is soft, yet supportive. In addition, seats that provide increased aeration through the seat surface tend to be more comfortable.
One type of seat that has been used is a fabric seat that is supported around the circumference by a seat frame. In this type of seat, the fabric is a membrane designed to provide increased aeration. Typically, these seats have been manufactured in an integrated molding operation, in which the outer edges of the fabric are secured to the seat frame by being molded into the seat frame. However, this manufacturing technique can be expensive and requires special manufacturing equipment that is not always readily available. Thus, a low cost fabric seat is desirable.